Treatment of enriched benzol wash oil or the like



Oct. 2G, i942. A. scHMALENBAcx-l TREATMENT OF ENRICHED BENZOL WASH-OIL OR THE LIKE Filed oct. '7, 1938 Patented Oct. 20, 1942 TREATMENT F ENRICHED BENZOL WASH OIL OR THE LIKE Adolf Schmalenbach, Essen, Germany, assignor, by mesne assignments, to Kopllers Company, Pittsburgh, Pa., a corporation of Delaware Application October 7, 1938, Serial No. 233,721 In Germany October 7, 1937 1 Claim.

The present invention relates tothe continuous treatment of liquids containing certain substances, for instance, wash oil enriched with benzol or other hydrocarbons, by means of distillation in the presence of steam vfor the recovery of valuable products from said liquids or wash oil.

For the recovery of benZol and other Valuable hydrocarbons from coal distillation gases or the like it is customary to wash the gas to be treated with a suitable solvent such as tar oil. The solvent or tar oil absorbs the benzol hydrocarbons which, after the oil is sufficiently enriched with hydrocarbons absorbed from the gas treated, are separated from the solvent'by a distillation in the presence of steam. The oil regenerated in this way may be used again for the gas Washing. The vapours of hydrocarbons driven off from the enriched wash oil are condensed and/or puried by rectification or by any other suitable treatment.

For the treatment of the enriched Wash oil, distillation in the presence of steam is generally used by means of which the boiling temperatures are reduced to such a degree that a dangerous decomposition of the valuable oil constituents is prevented. It is common practice to add, during the distillation in the presence of steam, so much steam that the wash oil and the wash oil vapours,

respectively, are not subject to a temperature l higher than to about 140 degrees centigrade. In order to maintain such low distillation temperatures it is necessary to distil in the presence of large amounts of steam but this, on the other hand, makes the fractionating of the vapours, i. e. the separation of the distillate into several fractions of sharply defined boiling limits, practically impossible. v

The main object of my invention is to develop improvements by means of which the problem of carrying out the continuous treatment of enriched benzol wash oil or the like, for the purpose of recovering hydrocarbons absorbed by the wash oil in several well dened fractions, is solved in such a manner that, although the distillation in the presence of steam is made use of and advantageously with regard to preventing the decomposition of the washing agent, the absorbed hydrocarbons are nevertheless obtained in various fractions of sharply defined boiling limits.

My present invention provides for this purpose substantially the process as set forth and eX- plained in the following:

First of all the absorbed hydrocarbons of the enriched Wash oil or the other solvent are driven off in continuous operation by distillation in the presence of steam, and the vapours thus distilling over are then condensed wholly or partly, Whereupon the condensate (primary product), after the Water is separated therefrom, is heated and vaporized in a continuous heater (pipe still), preferably to a temperature of about v23() to 240 C., and the vapours thus formed are introduced into a rectifier column with a small quantity of steam andtreated in sucha manner that at the top of the rectifier column, the vapours consisting of the lowest boiling constituents for instance crude benzol, escape, such vapours containing about 8% of steam or less (based upon benzol vapours).

A- distinct difference between the method of working according tothe .present invention and the heretofore known process, consists in that the so-called `primary products, that is, the mixture of wash oil and of hydrocarbons absorbed from the gas escaping from the distilling apparatus, are heated 4at a .comparatively high temperature (about 230-240" C. before the mixture is delivered tothe rectifier column. Thisdistilling temperature is vconsiderably higher than the temperature limit which .heretofore was considered as being permissible. Surprisingly it Was found, however, that the so-called primary product is able to vvithstand sucha high heat treatment Without .causing any dangerous effects upon the wash-oil contained therein. The Wash oil constituents in the primary product show a considerably lower tendency to decompose and this is probably due to the nature of the light hydrocarbons absorbed from the gas and present in large quantities in the primary product.

Another yimportant feature according to the present invention consists in limiting the addition of steam to the rectifier column. It was found .that with an addition of steam calculated according to the present invention it is possible to obtain at the top of the rectifier column an extraordinarily pure crude benZol or other low boiling fractions, and at other points of the column correspondingly sharp fractions -of another kind, such as toluol, solvent naphtha, and a residual oil highly enriched with naphthalene, from which the naphthalene crystallizes out .without any difficulty upon the cooling of the residue to normal temperature.

If based, for instance, upon benzol enriched wash oil containing 0.25% of water and 2.4% of constituents distilling over up to 180 C., and producing therefrom the so-called primary product which begins to boil at C. and which contains 45% of constituents distilling over up to 180 C.

by the method in which distillation is in the presence of steam, the vapours are cooled down, and the water is decanted, there can be recovered in the rectifier column the following fractions according to the process of my present invention:

Crude benzol:

Initial `boiling temperature 76 C. Final boiling temperature 108 C. 95-96% boiling up to 100 C.

Toluol: y

Initial boiling temperature 100 C. Final boiling temperature 128 C. 9596% boiling up to 120 C.

Solvent naphtha:

Initial boiling temperature 135 C. Final boiling temperature 195 C. 95% boiling up to 180 C.

Residual fraction rich in naphthalene: Initial boiling temperature 175 C. 0.15% boiling up to 180 C.

'I'he wash oil condensate (primary product) is thereby driven 'olf during vaporization in such a manner that the oil after such a treatment contains only 0.25% water and 0.15% constituents vboiling up to 180 C.

Still further objects and features of my present invention may be taken from the following description of a preferred embodiment thereof and lfrom the accompanying drawing which illustrates schematically an apparatus arrangement for carrying out the process Vaccording to the present invention.

The enriched Wash oil coming from the gas scrubber, not shown on the drawing, rst of all flows through the pipe line I into a heater 2 provided with coils, through lwhich the oil to be heated-flows. Here the wash oil'is very quickly heated, preferably to a temperature of about 160 to 180 C. It maybe noted that the oil Awill be heated without any harmful decomposition to a temperature somewhat higher than in the crdinary heating apparatus in which the oil is only slowly moved. A much higher temperature will therefore improve the action of driving olf of the hydrocarbons absorbed by the oil from the gas treated. The preheated wash oil treated in the furnace 2, which is similar to 'a known pipe still, then passes through the pipe line 3 into the distilling column 4 into which stream is added from below through the pipe line 5. The denuded wash oil, freed from the absorbed hydrocarbons, flows from the lowest section of the column 4 through the pipe line 6 into the collecting main 1 for denuded wash oil, and may be led back again to the gas scrubber, after suitable cooling down, or other treatment if desired.

The vapours developed in the column 4 flow through the pipe line 8 into the primary product cooler 9 where they are condensed. The condensate, i. e., the so-called primary product,

reaches a water separator I0 from where the conv densate, freed from waterl and consisting of a certain quantity of wash-oil and of the hydrocarbons absorbed by the oil both of which were driven off in the column 4, may be discharged through the pipe line I I.

The pipe line II leads to a heater I2 which is constructed similarly to a pipe still. The condensate is heated up in this pipe still so that it vaporizes. The temperature of the oil in the pipe still may be raised for instance to about 230- 240 C. I'he hot primary product and the vapours formed pass through the pipe line I3 into a rectifier column I4 into which a certain quantity of steam is introduced from below through the pipe line I5.

'I'he temperature of the oil at the inlet of the rectifier column I4, and the quantity of steam added through the pipe line I 5, are so calculated that the lower boiling hydrocarbons are evaporated, and that at the top of the column I4, through the pipe line I6, a vapour mixture is withdrawn which has a temperature of about (iQ-'72 C. This vapour mixture consists of a benzol yfraction boiling between 76 and 108 C.,

and of 8% steam or less, calculated upon the quantity of the benzol vapour. Said vapour mixture is condensed in a cooler I1. which, similarly to cooler 9, is connected with a water separator in such a manner that a crude benzol freed from water may be discharged at I8. A part of the crude benzol obtained in the cooler I'I may be suitably Adelivered as reflux at the top of the rectifier column I4.

Toluol vapours may be discharged at a lower point of the column I4 through the pipe line I9 leading to the cooler 20. Similarly the pipe line 2I and the cooler 22 serve for the recovery of the so-called solvent naphtha. Under certain conditions it may be advisable to connect in front of the coolers 20 and 22 a further auxiliary column in order to purify the vapours of toluol and solvent naphtha escaping from the column I 4 before the vapours are condensed.

It is further possible to extract from theV column I4 through the pipe line 23 a residual oil rich in naphthalene which, if the residual oil is cooled down to normal temperature (15 C.) Within the pan 24, crystallizes out readily. The mother liquor from such naphthalene crystallization in the pan 24, which mainly consists of certain wash oil constituents, flows through the pipe line 25 into the collecting main 'I for regenerated (denuded) wash oil.

The residual oil, freed from the low boiling constituents in the column I4, flows into the collecting main I through the pipe line 26.

In the foregoing I have described my invention on the basis of Wash oil treatment as used in the coal distillation industry, but I wish it clearly to be understood that the principle of my invention, i. e. the primary distillation of the enriched oil or solvent in the presence of steam at comparatively low temperatures, and the distillation of the condensate vapours from such primary distillates, after separating of the condensed water, by meansof a pipe still, or another similar distilling apparatus, may be advantageously used for the treatment of other washing media or solvent, such as the washing oil used for absorbing light hydrocarbons from other gases or vapours, and therefore my invention is in no way limited to the mode of carrying out as described and explained hereinbefore.

I have now above described my present invention on the lines of a preferred embodiment thereof but my invention is not limited in all its aspects to the mode of carrying it out as described and shown, since the invention may be variously embodied within the scope of the following claim.

I claim:

A process for the continuous treatment of lighthydrocarbon enriched Wash-oil of the character of benzol-absorbent wash-oil by distillation in the presence of steam with the recovery of the lighthydrocarbons from the absorbent wash-oil in several fractions of sharply defined broiling limits,

comprising the steps: distilling the light-hydrofractonating the vapours from the pipe still in a rectifying apparatus, and in which the vapors from the pipe still are fractionated with a limited quantity of steam in the fractionation step, the quantity of steam being such that at the top of the rectfyng column a miXure consisting of benzol and about 8% by Weight of steam or less (based upon the benzol vapours) ow off.

' ADOLF SCHMALENBACH. 

